Among working vehicles there are those mounted with what is called HST (Hydro Static Transmission). In an HST type working vehicle an engine drives a hydraulic pump and a traveling hydraulic motor is driven by hydraulic fluid discharged from a hydraulic pump. This is how the working vehicle is made to travel. In an HST type working vehicle, vehicle speed and tractive force can be controlled by controlling engine rotation speed, pump displacement of the hydraulic pump and motor displacement of the traveling hydraulic motor and the like. (See, Japan Patent Laid-open Patent Publication JP-A-2004-144254).
The working vehicle as described above can perform an upper limit speed variable control. The upper limit speed variable control is a control that limits the upper limit of vehicle speed to a speed that is lower than maximum vehicle speed. With such upper limit speed variable control the lower limit of motor displacement is limited to be a larger lower limit displacement than minimum displacement. In this way, upper limit vehicle speed is reduced to be below maximum vehicle speed. Further, the upper limit of vehicle speed is reduced as the lower limit of motor displacement is increased. In this way, an operator can freely set the upper limit vehicle speed at the desired speed.